GB2103874A

GB2103874A - A method of adjusting the resonant frequency of a coupled resonator

Info

Publication number: GB2103874A
Application number: GB08209176A
Authority: GB
Inventors: Hirofumi Kawashima
Original assignee: Seiko Instruments Inc
Current assignee: Seiko Instruments Inc
Priority date: 1981-05-15
Filing date: 1982-03-29
Publication date: 1983-02-23
Also published as: US4484382A; CH652563GA3; JPH0150129B2; DE3217721A1; GB2103874B; JPS57188121A

Abstract

Each resonant frequency of a coupling resonator is measured at a plurality of each different temperatures. From these values the first order temperature coefficient alpha is calculated. According to the value of alpha , it is accurately adjusted and finally the resonant frequency of a fundamental vibration is also adjusted to a nominal frequency.

Description

1 GB 2 103 874 A 1,

SPECIFICATION

A method of adjusting the resonant frequency of a coupled resonator The present invention relates to a method of adjusting the resonant frequency of a resonator having a plurality of coupled vibrational modes, such a resonator being known as a coupled resonator.

There are many consumer products requiring resonators having excellent temperature characteristics, in which an AT cut quartz resonator has been used. Recently, however, numbers of consumer products are miniaturized. Therefore a miniaturized AT cut quartz resonator is also required. However, resonators of this type 80 suffer from spurious vibrations and their miniaturization is difficult.

In particular, if an AT cut quartz resonator is used in a wrist watch, corresponding miniaturization of this resonator is required and consequently its size is not sufficient when compared with that of a flexural quartz resonator of the tuning fork type.

Recently, resonators have been produced by means of a photographic process applied to an IC (integrated circuit) production. As a result, it is possible to provide extremely small resonators. For example, this process may be applied to a GT cut quartz resonator which has excellent frequency-temperature characteristics and which 95 is extremely thin, and it may also be applied to a flexural-torsional quartz resonator (called an FT quartz resonator hereinafter) in which a torsional vibration is coupled to a flexural vibration.

However, in order to ensure that these GT cut and 100 FT cut quartz resonators have excellent frequency-temperature characteristics, they make use of two vibrational modes, that is to say, a fundamental vibration is coupled to a sub vibration. Therefore, the temperature characteristics are determined by the frequency difference of the fundamental vibration and the sub-vibration and by the intensity of each vibration. In particular, as the ratio of the intensities of the fundamental vibration and the sub-vibration differs there is a corresponding difference in the resonant frequency at which excellent frequency-temperature characteristics can be provided. (Such characteristics will hereinafter be referred to as "temperature 115 characteristics"). Consequently it is necessary to adjust the difference between the resonant frequencies of each resonator. However, this adjustment is time-consuming, causes high costs, and is unsuitable for mass production and this 120 may well be one of the reasons that resonators of this type are not used in many fields.

According, therefore, to the present invention, there is provided a method of adjusting the resonant frequency of a resonator having a 125 plurality of coupled vibrational modes, the said method comprising measuring the resonant frequencies of a fundamental vibration of the resonator at a plurality of different temperatures; calculating a frequency-temperature coefficient a of the first order from the said measured resonant frequencies; adding weight to or removing it from the resonator so as to make the coefficient a approximately zero; and then adjusting the resonant frequency of the fundamental vibration of the resonator to a desired nominal frequency.

The weight may be removed by means of a laser or may be added by evaporation equipment. In either case, a coupled resonator having optimum temperature characteristics and optimum resonant frequency may first be produced before the resonant frequency is adjusted, and resonant frequencies fl, f2 of the fundamental vibration may be respectively measured at arbirary temperatures tl, t2. On the basis of these measurements the first order temperature coefficient a may be calculated, and then, by utilizing the laser or evaporation equipment, the first order temperature coefficient a may be adjusted to substantially zero and moreover, the resonant frequency of the fundamental vibration may also be adjusted to the desired nominal frequency f., As a result, it is possible to provide a GT cut quartz resonator which has excellent temperature characteristics and which enables high accuracy wrist watches to be produced. As the first order temperature coefficient is adjusted after the temperature characteristics of each resonator is measured, the percentage of defective resonators which are rejected because of defective temperature characteristics is substantially reduced, whereby costs are reduced.

The resonator preferably has a rectangular vibrating portion on one pair of opposite sides of which there are integral support portions.

The support portions may be mounted on a pedestal.

The rectangular vibrating portion is preferably provided with a plurality of weights adjacent the other pair of opposite sides thereof.

Thus there may be one pair of weights which are disposed centrally of the said other pair of opposite sides, and two further pairs of weights each pair of which is disposed between the said one pair of weights and respective corners of the rectangular vibrating portion.

The resonator may be GT-cut quartz resonator or an FT quartz resonator.

The invention also comprises a resonator whose resonant frequency has been subjected by the method set forth above.

The invention is illustrated, merely by way of example, in the accompanying drawings, in which:- Figures 1 A and 1 B show the shape and electrodes of a coupled resonator, e.g. a GT-cut quartz resonator, Figures 1 A and 1 B showing a front view and a bottom view, Figures 2A and 213 show a GT-cut quartz resonator of the kind shown in Figures 1 A and 1 B mounted on a pedestal, Figures 2A and 213 respectively showing a front view and a bottom view, 2 GB 2 103 874 A 2 Figure 3 is a graph illustrating the temperature characteristics of the GT-cut quartz resonator which has been formed by a photo-lithographic process, Figure 4 shows a front view of a GT-cut quartz 70 resonator having a particular arrangement of weights thereon, Figure 5 is a graph which shows the relationship between the first order temperature coefficient a and the extent to which the weights 75 shown in Figure 4 are removed by laser equipment, Figure 6 shows a front view of a GT-cut quartz resonator having weights at the four corners of its rectangular vibrating portion, Figure 7 is a graph which shows the relationship between the first order temperature coefFicient a and the extent to which the four weights shown in Figure 6 are removed by making use of the laser equipment, Figure 8 shows a front view of another GT-cut quartz resonator having a different arrangement of weights, Figure 9 is a graph which shows the relationship between the first order temperature 90 coefficient a and the extent to which the weights shown in Figure 8 are removed by the laser equipment, Figure 10 is a graph which shows the relationship between the resonant frequency of 95 the fundamental vibration and the extent to which the weights shown in Figure 8 are removed by the laser equipment, Figure 11 shows a front view of a GT-cut quartz resonator having a particular arrangement 100 of weights thereon so that excellent temperature characteristics can be obtained by adjusting the resonant frequency, Figure 12 is a graph illustrating the temperature characteristics of a resonator which 105 has been formed by etching, the characteristics being measured before the resonant frequency is adjusted, Figure 13 is a graph illustrating the adjustment of the temperature characteristics of a GT quartz 110 resonator, and Figure 14 is a graph illustrating the adjustment of the temperature characteristic of a GT-cut quartz resonator by the laser method.

Figures 1 A and 1 B show the shape and the electrodes of one practical embodiment of a coupled resonator having two coupled modes, e.g. a mode coupled GT-cut quartz resonator.

Figures 1 A and 1 B show a front view and a bottom view respectively of the resonator.

Electrodes 2, 3 are disposed on obverse and reverse sides respectively of a quartz member 1.

The resonator of Figures 1 A and 1 B may be easily excited by applying an alternating voltage to the electrodes 2, 3. Moreover, the resonant frequencies of the two coupled modes are determined by the width W and the length L of the quartz member 1. The resonant frequency of the fundamental vibration which is determined by the width W will be given the symbol fw, and the 130 resonant frequency of the sub-vibration which is determined by the length L will be given by the symbol fl.' The temperature characteristics of the resonator are determined by the difference of the resonant frequencies (fW-fL) and also by the intensities of the fundamental vibration and the sub-vibration.

As will be seen, the resonator shown in Figures 1 A and 1 B comprises a centrally disposed rectangular vibrating portion 1 a one pair of opposite sides 1 b thereof being integral with support portions 1 c.

Figures 2A and 2B show a GT-cut quartz resonator of the kind shown in Figures 1 A and 1 B mounted on a pedestal, Figures 2A and 2B being a front view and a bottom view respectively.

Support portions 5a of a quartz resonator 5 are mounted on a pedestal 4 and are adhered to the pedestal by adhesives or by solder at end portions 8, 9 of the resonator 5. Electrodes 6, 7 for exciting the GT-cut quartz resonator 5 are disposed on the observe and the reverse sides of the resonator 5.

Figure 3 is a graph illustrating the temperature characteristics of a GT-cut quartz resonator which is formed by a photo-lithographic process and on which no weights have been added for adjusting the resonant frequency of the resonator. The temperature characteristics of the resonator differ according to the coupling intensity. When the coupling between the fundamental vibration and the sub-vibration is weak, the temperature characteristics are shown by a straight line a, and when the coupling between the fundamental vibration and the sub-vibration is strong, the temperature characteristics are shown by a straight line b. The absolute value of the first order temperature coefficient a is approximately 2.5x 10-6/IC. This is too large and the straight lines a, b do not show excellent temperature characteristics. In general, resonators formed by a photo-lithographic process have such temperature, characteristics. If the resonant frequency of the fundamental vibration is adjusted by using a laser after having previously added weights to the resonator, the value of the first order temperature coefficient a is somewhat different, but even in this case it has almost the same value.

Figure 4 shows an embodiment of the GT- quartz resonator on which weights are disposed. Weights 10, 11 are disposed on a centrally disposed rectangular vibrating portions 1 Oa of the resonator adjacent to and midway of the sides 1 Ob thereof and thus, with respect to the symmetry of the central vibrating portion 1 Oa at the end portions in the width direction and at the central portions in the length direction. The thickness of the weights is between about 1 pm and 2 pm.

Figure 5 shows the relationship between the amount of the weights which are removed and the first order temperature coefficient a when the weights 10, 11 shown in Figure 4 are removed by laser equipment. That is to say, as the amount of the weights which are removed is increased, the 3 GB 2 103 874 A 3 first order temperature coefficient a shifts to a positive value.

Figure 6 shows an embodiment of a GT-cut quartz resonator having four weights 12, 13, 14, 15 which are respectively disposed at the four corners of the central rectangular vibrating portion of the resonator.

Figure 7 shows the relationship between the amount of the weights which are removed and the first order temperature coefficient a, when the 75 four weights 12, 13, 14, 15 shown in Figure 6 are removed by making use of laser equipment. As the amount of weights which are removed is increased, the first order temperature coefficient a shifts to a negative value.

As will be understood from these results, if the weights are disposed as shown in Figure 4, and these weights are removed, the first order temperature coefficients a shifts to a positive value, while if the weights are disposed as shown 85 in Figure 6 and these weights are removed, the first order temperature coefficient a shifts to a negative value. Consequently if weights are disposed in positions between the weights 10, 11 shown in Figure 4 and the weights 12, 13, 14,15 90 shown in Figure 6, and these weights are removed, it is possible to arrange that the first order temperature coefficient a does not shift at all. Figure 8 therefore shows a front view of another example of the disposition of the weights 95 of a GT-cut quartz resonator.

As shown in Figure 8, weights 16, 19 are disposed in positions between the weight 10 shown in Figure 4 and the weights 12, 15 shown in Figure 6, and weights 17, 18 are disposed in positions between the weight 11 shown in Figure 4 and the weights 13, 14 shown in Figure 6.

Figure 9 shows the relationship between the amount of the weights which are removed and the first order temperature coefficient a, as the weights 16, 17, 18, 19 shown in Figure 8 are removed by the laser equipment. As will be appreciated, as the weights 16-19 are removed, the first order temperature coefficient a does not shift at all.

Figure 10 shows the relationship between the resonant frequency of the fundamental vibration 110 of the resonator and the amount of the weights which are removed. It will be appreciated that, as the weights 16, 17, 18, 19 shown in Figure 8 are removed by the laser equipment, the resonant frequency of the fundamental vibration will increase.

Figure 11 shows how the weights maybe disposed that a GT-cut quartz resonator may be provided with excellent temperature characteristics by adjusting the resonant frequency. Weights 24, 25 are provided adjacent the mid points of opposite sides of the rectangular vibrating portion of the resonator for adjusting the temperature characteristics, and weights 20, 21, 22, 23 (which are positioned similarly to the weights 16-19 of Figure 8) are provided for adjusting the resonant frequency of the fundamental vibration. Thus there are one pair of weights 24, 25 which are disposed centrally of the pair of sides of the rectangular vibrating portion remote from the pair of sides thereof which are integral with the support portions, and there are two further pairs of weights 20, 2 1, and 22, 23 each pair of which is disposed between the pair 24, 25 and the respective corners of the rectangular vibrating portion.

The following description relates to a method of adjusting the frequency. As the GT-cut quartz resonator shown in Figure 11 is formed by a photo-] ithograph ic process, it is designed as follows:- (1) The first order temperature coefficient a has a negative value, that is to say, as the temperature rises the resonant frequency decreases, (2) The resonant frequency of the fundamental vibration is lower than the nominal frequency to which it is to be adjusted.

Such a resonator may be easily produced by appropriate selection of its shape, quantity of weights, and time for which it is etched.

Figure 12 shows the temperature characteristics of a resonator which has been measured after the resonator has been formed by etching symbol C shows the amount of deviation from the nominal frequency, the resonant frequency of the resonator being lower than the nominal frequency. The resonator is maintained at an arbitrary temperature, the said arbitrary temperature, which is given the symbol tp is read by a thermometer and the resonant frequency fl of the fundamental vibration of the resonator is measured at the temperature tV Next, the resonator is maintained at another temperature, which is read in the same way and is given the symbol tV the resonant frequency f2 of the fundamental vibration being also measured at the temperature t2.

At the temperatures tV t2 and the resonant frequencies fl, f2, the first order temperature coefficient a is calculated by the following equation:f2-fl a-(Hz/IC) (1) t2-t 1 Moreover, by making use of the nominal frequency f. to which the resonator is to be adjusted, the equation (1) can be rewritten as follows- f2-fl 1 a- (i/-C) (2) fo t2-tl Figure 13 illustrates a method according to the present invention of adjusting the temperature characteristics of a GT-cut quartz resonator. After measuring the resonant frequencies fl, f2 at the temperature tl, t2, the first order temperature coefficient a is calculated by utilizing the equation (2).

4 GB 2 103 874 A 4 For the example described above, the first order temperature coefficient a is calculated from the temperatures tj, t2 and resonant frequencies fl, f2. However, if greater accuracy is required in the measurement of a, this may be achieved by the number of temperatures and resonant frequencies of the fundamental vibration used in the calculation of a and even greater accuracy may be achieved by the use of the minimum square method.

In order to make the first order temperature coefficient a approach zero, as explained with reference to Figures 4 and 5, the weights 24, 25 shown in Figure 11 (which correspond to the weights 10, 11 of Figure 4) are removed and, as a result, the characteristic represented by a straight line e shown in Figure 13 changes to that represented by a dotted line f. Moreover, by continuing the adjustment, there is obtained the characteristic represented by a straight line g whose first order temperature coefficient is almost zero. Then, the resonant frequency of the fundamental vibration approaches the nominal frequency f. more and more.

Next, it is possible to adjust the resonant frequency of the fundamental vibration to the nominal frequency fo at room temperature by removing the weights 20, 21, 22, 23 shown in Figure 11 without changing the temperature characteristics. Consequently, it is possible to provide a resonator which has excellent temperature characteristics and whose resonant frequency of the fundamental vibration is adjusted to the target value, i. e. the nominal frequency. In the above description reference has been made to 100 removing weights by means of a laser, but it is also possible to add weight by means of an evaporation method. That is to say, the resonator may be formed by etching without providing the resonator with any weights, the resonator being designed as follows:(1) The first order temperature coefficient a has a positive value, in other words, as the temperature rises, the resonant frequency rises. 45 (2) The resonant frequency of the fundamental vibration is higher than the nominal frequency to which the resonator is to be adjusted. Such a resonator is also easily obtained by appropriate selection of its shape and length of time for which it is etched. The resonant frequencies fl, f2 of the fundamental vibration are respectively measured at different arbitrary temperatures tj, t2 The first order temperature coefficient a is calculated by making use of the question (1) or (2). Next, the weights 24, 25 are deposited on the 120 resonator at the positions shown in Figure 11. As the first order temperature coefficient a is shifted to a negative value by the deposition of the weights, it is possible to make a substantially zero. After that, by depositing the weights 20, 21, 125 22, 23 at the positions shown in Figure 11, it is possible to adjust the resonant frequency of the fundamental vibration to the nominal frequency fo without changing the temperature characteristics.

In the same way as in the laser method described above, it is possible to provide a coupled resonator which has excellent temperature characteristics and in which the resonant frequency of the fundamental vibration is adjusted to the nominal frequency %.

Figure 14 illustrates the temperature characteristics of a GT-cut quartz resonator wherein a straight line h shows the temperature characteristic before the resonant frequency is adjusted by the laser equipment, and a curve 1 shows the temperature characteristic as measured after the resonant frequency has been adjusted by the laser equipment. It will be appreciated that excellent temperature characteristics are indicated by the curve 1 shown in Figure 14.

As described above, in either the case of the laser method or the case of the evaporation method, first of all, a coupled resonator having optimum temperature characteristics and an optimum resonant frequency is made before the resonant frequency is adjusted and the resonant frequencies fl, f2 of the fundamental vibration are measured at the arbitrary temperatures tj, t2. On the basis of these values the first order temperature coefficient a is calculated, and then, by utilizing laser or evaporation equipment, the first order temperature coefficient a is adjusted to approximately zero and moreover, the resonant frequency of the fundamental vibration is adjusted to the nominal frequency f.. As a result, it is possible to provide a GT-cut quartz resonator having excellent temperature characteristics. Therefore, the use of such a GT- cut quartz resonator makes it possible to realize high accuracy wrist watches. As the first order temperature coefficient is adjusted after measuring the temperature characteristics of each resonator in either of these methods, there is a remarkable reduction in the percentage of resonators which have to be rejected because of the defective temperature characteristics. These methods, therefore, make it possible to reduce the cost of the resonators.

In the above description, reference has been made to the GT-cut quartz resonator, but of course the present invention is easily applicable to other coupled resonators, e.g. to FT quartz resonators.

Claims

1. A method of adjusting the resonant frequency of a resonator having a plurality of coupled vibrational modes, the said method comprising measuring the resonant frequencies of a fundamental vibration of the resonator at a plurality of different temperatures; calculating a frequency-temperature coefficient cr of the first order from the said measured resonant frequencies; adding weight to or removing it from the resonator so as to make the coefficient a approximately zero; and then adjusting the resonant frequency of the fundamental vibration of the resonator to a desired nominal frequency.

GB

2 103 874 A 5 2. A method as claimed in claim 1 in which the weight is removed by means of a laser.

3. A method as claimed in claim 1 in which the weight is added by an evaporation method.

4. A method as claimed in any preceding claim in which the resonator has a rectangular vibrating portion on one pair of opposite sides of which there are integral support portions.

5. A method as claimed in claim 4 in which the support portions are mounted on a pedestal.

6. A method as claimed in claim 4 or 5 in 45 which the rectangular vibrating portion is provided with a plurality of weights adjacent the other pair of opposite sides thereof.

7. A method as claimed in claim 6 in which there are one pair of weights which are disposed centrally of the said other pair of opposite sides, and two further pairs of weights each pair of which is disposed between the said one pair of weights and respective corners of the rectangular vibrating portion.

8. A method as claimed in any preceding claim in which the resonator is a GT-cut quartz resonator.

9. A method as claimed in any of claims 1-7 in which the resonator is an FT quartz resonator. 60

10. A method as claimed in any preceding claim and substantially as described with reference to Figure 11.

11. A resonator whose resonant frequency has been adjusted by the method claimed in any 65 preceding claim.

12. A method of adjusting resonant frequency of a coupling resonator which is coupled with a plurality of vibrational modes, in which a process of measuring each resonant frequency of a fundamental vibration at a plurality of each different temperature, next, a process of calculating a frequency- temperature coefficient of the first order a by use of a plurality of each different temperature and each resonant frequency of a fundamental vibration, then, a process of adding weights on the resonator or eliminating weights disposed on the resonator so as to lead the first order temperature coefficient a to almost zero and a process of adjusting the resonant frequency of the fundamental vibration to nominal frequency fo.

13. A method of adjusting resonant frequency of a coupling resonator which is coupled with a plurality of vibrational modes, in which, setting said resonator at arbitrary temperature tj, a process of measuring resonant frequency fl of a fundamental vibration at the arbitrary temperature tj, next, setting said resonator at another temperature tV a process of measuring resonant frequency f2 of said fundamental vibration at the another temperature tV a process of calculating a frequency- temperature coefficient of the first order a by means of the temperatures tj, t2 and the resonant frequencies f,, f2, then, a process of adding weights on the resonator or eliminating weights disposed on the resonator so as to lead the first order temperature coefficient a to almost zero and a process of adjusting the resonant frequency of the fundamental vibration to nominal frequency fo.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1983. Published by the Patent Office. 25 Southampton Buildings, London, WC2A IlAY, from which copies may be obtained